1. Field of the Invention
The present invention relates to an X-ray mask suited to proximity X-ray lithography for use in semiconductor production, a method of manufacturing the same, and an X-ray exposure method.
2. Discussion of the Background
With the recent shrink in feature size of semiconductor integrated circuits, a proximity X-ray lithography exposure method by which a mask and a wafer substrate are placed close to each other and mask patterns are transferred onto the wafer substrate by using X-rays having a short wavelength has been proposed.
A suitable wavelength region of a light source used in actual proximity X-ray lithography is determined by Fresnel diffraction controlling the resolution of the transfer pattern and the secondary electrons generated in the substrate by X-rays. The narrower the gap between the mask and the wafer and the shorter the exposure wavelength, the smaller the diffraction of light and the higher the resolution. On the other hand, the secondary electrons such as photoelectrons and associated Auger electrons increase and affect the exposure in a resist when short-wavelength X-rays are used in exposure, and these secondary electrons lower the resolution. From the relationship between these diffraction effect and secondary electron effect, therefore, the exposure wavelength of X-rays used is preferably 0.6 to 1 nm in terms of resolution, so it is desirable to use X-rays of 0.6 to 1 nm in exposure.
In actual exposure system and conventional X-ray masks, however, an absorber material of the masks suited principally to one specific wavelength is assumed. Therefore, no examinations have been done for an absorber and an X-ray mask suitable for synchrotron radiation having a wavelength region between 0.6 and 1 nm. Since the absorption and phase properties of materials greatly depend upon the X-ray wavelength used, a material must be so selected as to meet the wavelength used in exposure. However, synchrotron radiation has a continuous spectrum with a wide wavelength region, so a suitable absorber and mask material vary from one spectral characteristic to another. No prior art considers this point.
For example, Jpn. Pat. Appln. KOKAI Publication No. 5-13309 has proposed a technique which performs exposure to X-rays having a wavelength of 1 to 1.5 nm by using Co, Ni, Cu, Zn, and their alloys as absorber materials. However, this reference describes only the absorption of Co, Ni, Cu, and Zn at one specific wavelength of 1.225 nm, as the wavelength of the above wavelength region, and the absorber film thickness at a mask contrast of 10. That is, this reference does not take account of absorption characteristics, phase shift characteristics, and mask contrast obtained when exposure is performed by synchrotron radiation with a wide wavelength region of 0.6 to 1 nm, and optimization of the exposure wavelength when X-ray exposure and pattern-transfer is actually performed by using these absorber materials. According to the technique of this reference, the wavelengths of the absorption edges of the respective elements exist within the X-ray wavelength region of 1 to 1.5 nm. So, these elements are unsuited to improving the absorption characteristics and phase shift characteristics.
Accordingly, it is an object of the present invention to provide an X-ray mask which, in proximity X-ray lithography using synchrotron radiation having a maximum light intensity of light entering a mask unit at a wavelength of 0.6 to 1 nm, can decrease the film thickness of an absorber by the use of a material having large absorption in this exposure wavelength region and thereby can contribute to, e.g., improvements of the exposure accuracy in the X-ray exposure, a method of manufacturing the same, and an X-ray exposure method.
It is another object of the present invention to provide an X-ray mask which, in X-ray exposure using synchrotron radiation having a maximum light intensity of light entering a mask unit at a wavelength of 0.6 to 1 nm, can improve the resolution of transfer patterns by the use of a material having a controlled phase shift amount and thereby can contribute to, e.g., improvements of the exposure accuracy in the X-ray exposure, a method of manufacturing the same, and an X-ray exposure method.
According to one aspect of the present invention, there is provided an X-ray exposure method comprising supporting an X-ray mask unit in which a patterned X-ray absorber is formed on a membrane, the patterned X-ray absorber containing one of an element having a density/atomic weight of not less than 0.085 [g/cm3] and an L-shell absorption edge at a wavelength of 0.75 to 1.6 nm and an element having a density/atomic weight of not less than 0.04 [g/cm3] and an M-shell absorption edge at a wavelength of 0.75 to 1.6 nm; and applying synchrotron radiation having maximum light intensity at a wavelength of 0.6 to 1 nm onto the X-ray mask unit.
According to another aspect of the present invention, there is provided an X-ray exposure method comprising supporting an X-ray mask unit in which a patterned X-ray absorber is formed on a membrane, the patterned X-ray absorber being formed of one of an alloy and a multi-layer film, which comprises a first material containing an element having an L-shell absorption edge or an M-shell absorption edge at a wavelength of 0.75 to 1.6 nm and a second material containing an element having an M-shell absorption edge at a wavelength of 0.5 to 0.75 nm; and applying synchrotron radiation having maximum light intensity at a wavelength of 0.6 to 1 nm onto the X-ray mask unit.
According to still another aspect of the present invention, there is provided an X-ray exposure method comprising supporting an X-ray mask unit in which a patterned X-ray absorber is formed on a membrane, the patterned X-ray absorber being a material containing as a major constituent an element having all L- and M-shell absorption edges in a region shorter than the shortest wavelength or longer than the longest wavelength of an exposure wavelength region having an intensity not less than {fraction (1/10)} the light intensity at a wavelength of maximum light intensity of synchrotron radiation to be incident; and applying the synchrotron radiation onto the X-ray mask unit.
According to another aspect of the present invention, there is provided an X-ray mask comprising a membrane; and a patterned X-ray absorber formed on the membrane, wherein the patterned X-ray absorber is formed of one of an alloy and a multi-layer film, which comprises a first material having all L- and M-shell absorption edges in a region shorter than the shortest wavelength or longer than the longest wavelength of an exposure wavelength region having an intensity not less than {fraction (1/10)} the light intensity at a wavelength of maximum light intensity of synchrotron radiation to be incident and having one absorption edge in a wavelength region from the shortest wavelength of the exposure wavelength region to a wavelength shorter by 0.4 nm than the shortest wavelength, and a second material having all L- and M-shell absorption edges in a region shorter than the shortest wavelength or longer than the longest wavelength of the exposure wavelength region and having one absorption edge in a wavelength region from the longest wavelength of the exposure wavelength region to a wavelength longer by 0.6 nm than the longest wavelength.
According to still another aspect of the present invention, there is provided a method of manufacturing an X-ray mask, comprising supporting a mask substrate including a first X-ray transparent layer, a second X-ray transparent layer as a patterning layer formed on the first X-ray transparent layer; forming an X-ray absorber film in a concave portion of the second X-ray transparent layer; and polishing an unnecessary portion of the X-ray absorber film while applying a pressure by fluid from a side of the mask substrate opposite to the first X-ray transparent layer.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.